The process of the formation of a visible track in a nuclear research emulsion is approximated by a simplified model which reduces it to a one-dimensional problem. Within this basic approximation, there are included many different detailed models, including all models so far proposed in the literature. We then consider the following quantities characteristic of the track : the number of gaps longer than some minimum length r contained in a cell length t of the track, nr(t) ; and the sum of the excess (over and above r) lengths of these nr gaps, xr(t).